So radical, in fact, that parts of it met resistance from not only Senate Democrats, but even pro-enviro Obama folks.

And, notably, Jackson’s departure comes just as probes are heating up into her potential misuse of private e-mails to evade federal transparency rules.

A pillar of Jackson’s agenda was the so-called cap-and-trade bill, meant to curb greenhouse emissions. The bill died in 2010 when even Senate Democrats realized the damage it would do to the economy.

Alas, Jackson had a Plan B: She’d impose regulations by fiat — and to hell with Congress. Under her guidance, EPA devised the first-ever greenhouse-gas standards for vehicles and set onerous emissions rules for factories and power plants, particularly those that burned coal.

Coal-producing states like Kentucky, West Virginia and Pennsylvania understandably began to sweat, believing the entire industry was doomed — as were thousands of its jobs.

As it turned out, a federal court blocked her power-plant rule. And her most ambitious gambit, smog regulation, was scuttled by a re-election-focused President Obama, who feared that, in a weak economy, the plan would send precisely the wrong message to the nation’s job-producers.

Feeling “blindsided,” she almost quit.

Yet, there was a bright spot in Jackson’s record: She was an unabashed supporter of fracking, the controversial method of extracting gas and oil from rock formations deep below the surface.

Indeed, she blessed it as both safe and economically invaluable.

That was good news for New Yorkers, who’ve been waiting years for Albany to OK the process here and jolt the economy upstate.

But who knows if Jackson’s replacement will be as supportive of fracking?

Or as radical on other issues. (On these, admittedly, it will be hard to top Jackson.)

A great deal — for New York and the nation — now hangs in the balance.